The brain mechanisms that generate sleep and the functions served by sleep remain among the great Proposed studies will assess predictions concerning the behavior of sleep-active WSNs recorded in freely-moving rats. First, because of the circadian influences on sleep these neurons are predicted to exhibit changes in excitability and activity correlated with circadian rhythms in sleep propensity. Second, because of the potent homeostatic regulation of sleep, these neurons are predicted to show increased activity and excitability after sleep deprivation. We will also map the anatomical distribution of these neurons. Neurons containing the inhibitory neurotransmitter, gama-aminobutyric acid (GABA) are distributed within the POAH and adjacent sites containing WSNs. There is evidence for increased GABA release during NREM sleep. POAH WSNs have inhibitory outputs. We will assess the hypothesis that putative hypnogenic sleep-active WSNs are GABAergic, using intracellular labeling in anesthetized animals and immunostaining for GABA. If these hypotheses are confirmed, we can construct a detailed model of NREM control and indications of sleep function. Disorders involving sleep abnormalities such as depression and narcolepsy may then be understood in mechanistic terms.